Over the past decade, engineers have been trying to build more effective solar panels using “quantum dots” — semiconducting crystals that are only billionths of a metre across. These dots have the potential to absorb light energy extremely efficiently because, by changing their size, they can be tuned to absorb specific wavelengths.
But the main obstacle is that the kind of dot often used for solar cells, known as “n-type dots”, become oxidized and lose their ability to function within minutes of air exposure. To counter this, a team of engineers — including members at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia — created a robust protective layer coating by binding a single iodine atom to each dot. This shield is small enough that it does not block energy conversion, explains Zhijun Ning, an engineer at the University of Toronto, Canada, who led the study.
In a paper published in Nature Materials1, the team reports that the coated n-type dots survived in air for four days before losing functionality. “A record photocurrent was realized and the power conversion efficiency of 8% is among the best reported,” says Ning.
The team has also shown that the technique could be used for a very different application: sensing gases. If a film of coated quantum dots is connected by gold metal contacts, the electricity flow between the contacts increases in the presence of nitrogen dioxide. “[This] could potentially be applied to the sensing of pollutants and dangerous gases,” says Ning.